A circuit pattern is formed on a semiconductor integrated circuit or a printed board through a multitude of complicated steps of forming a film of a resist material on the surface of a base material, exposing a predetermined portion to light, removing an unnecessary portion through etching, and washing the surface of a substrate. Therefore, in the semiconductor industry, a resist at a necessary portion has recently been left and used as an insulating material as it is even after formation of a pattern through exposure and development so as to decrease the steps.
As the material, for example, heat resistant photosensitive materials such as a photosensitive polyimide and a photosensitive polybenzoxazole have been developed and put into practical use. Particularly, negative photosensitive polyimides to be developed with an organic solvent are used by many device manufacturers because of excellent heat resistance and ease of removal of impurities. With respect to these negative photosensitive polyimides, there is known a method in which a compound having a photosensitive group is added to or mixed with a polyimide precursor and a pattern is formed by a photocrosslinking reaction. However, these negative photosensitive polyimides do not cope with development with an aqueous alkaline solution (for example, development with an aqueous sodium tetramethylammonium solution) which has recently been used from consideration for the environment because of its material design coping basically to development with an organic solvent. Therefore, since the negative photosensitive polyimides are inferior in solubility in the case of developing with an aqueous alkaline solution, it was difficult to form a pattern. To obtain a negative photosensitive polyimide which can be developed with an aqueous alkaline solution, it is required to include an alkaline soluble group, and thus there is proposed an alkaline negative development type photosensitive polyimide precursor in which a photoreactive group is introduced into a portion of the alkaline soluble groups of a polyimide precursor. However, in this technique, since solubility in an alkaline developing solution of a polyimide precursor deteriorates as a result of introduction of a photoreactive group, it was difficult to form a pattern having a favorable shape with good reproductivity after development. Even if a pattern having a favorable shape can be formed, in the case where the polyimide precursor is finally converted into a polyimide, large curing shrinkage of the film involved in a ring closure reaction occurs. In the case of using in the form of a thick film having a thickness of 20 μm or more, cracking occurred and thus it was difficult to use.
Therefore, there is proposed a method in which no photoreactive group is introduced into the polymer and a photo acid generator, or a photo acid generator and an acid crosslinking agent are added to obtain a photosensitive polyimide composition (see, for example, Patent Document 1 and Patent Document 2). However, according to these methods, it was difficult to form a minute pattern having a shape with good reproductivity.
Also, there is proposed a method in which a polymerizable compound and a photopolymerization initiator are added to a binder polymer to obtain a negative pattern (see, for example, Patent Documents 3 to 6). However, according to these methods, a favorable pattern was not obtained, or a film having sufficient strength, elongation or heat resistance could not be obtained, sometimes.    [Patent Document 1] Japanese Unexamined Patent Publication (Kokai) No. 2003-98667 (pages 1-4)    [Patent Document 2] Japanese Unexamined Patent Publication (Kokai) No. 10-316751 (pages 1-4)    [Patent Document 3] Japanese Unexamined Patent Publication (Kokai) No. 2002-268215 (pages 1-3)    [Patent Document 4] Japanese Unexamined Patent Publication (Kokai) No. 2003-248306 (pages 1-3)    [Patent Document 5] Japanese Unexamined Patent Publication (Kokai) No. 2004-294553 (pages 1-4)    [Patent Document 6] Japanese Unexamined Patent Publication (Kokai) No. 2003-140339 (pages 1-3)